Dye laser tunable by longitudinal dispersion in the dye cell

ABSTRACT

A single mirror serves both as the output mirror for the pumping gas laser and the high reflectance mirror for the dye laser. THe mirror is formed on one surface of a lens having a low dispersion characteristic. The dye cell is positioned at the focus of the lens on the opposite side of the lens from the common mirror. The output of the dye laser is taken through a second mirror formed on an output lens of high dispersion material. Tuning is done by moving the output lens toward and away from the dye cell, or by varying the tilt of an etalon plate positioned between the dye cell and the output lens, or both.

United States Patent Hercher et al.

[ 1 Dec. 26, 1972 [72] Inventors: Michael Hercher; Harold Alan Pike,

both of Rochester, N.Y.

[73] Assignee: Spectra Physics, Inc., Mountain View, Calif.

[22] Filed: Dec. 29, 1970 [21] Appl. No.: 102,285

[52] U.S. Cl ..33l/94.5 [51] Int. Cl ..H0ls 3/08 [58] Field of Search..33 I/94.5

[56] References Cited UNITED STATES PATENTS 3,422,370 1/1969 Collins,Jr. ..33l/94.5

OTHER PUBLICATIONS Sorokin et al., End-Pumped Stimulated Emission from aThiacarbocyanine Dye. IBM Journal (Sept. 1966) pg 401,

Sorokin et al., Laser-Pumped Stimulated Emission from Organic Dyes:Experimental Studies and Analytical Comparisons. IBM Journal (Mar. I967)Primary Examiner-William L. Sikes Attorney-Hoffman Stone [57] ABSTRACT Asingle mirror serves both as the output mirror for the pumping gas laserand the high reflectance mirror for the dye laser. The mirror is formedon one surface of a lens having a low dispersion characteristic. The dyecell is positioned at the focus of the lens on the opposite side of thelens from the common mirror. The output of the dye laser is takenthrough a second mirror formed on an output lens of high dispersionmaterial. Tuning is done by moving the output lens toward and away fromthe dye cell, or by varying the tilt of an etalon plate positionedbetween the dye cell and the output lens, or both.

2 Claims, 1 Drawing Figure PATENTED DEC 2 6 I972 INVENTORS MICHAELHERCHER BY H. ALAN QPj/ig ATTORNEY DYE LASER TUNABLE BY LONGITUDINALDISPERSION IN THE DYE CELL BRIEF DESCRIPTION ficient operation,especially when continuous output is desired, they must be pumped byanother laser, rather than by ordinary light. See, for example, thefollowing articles:

Lasers Based on Solutions of Organic Dyes by B. I. Stepanov and A. N.Rubinov, Soviet Physics Uspekhi, Volume II, page 304, 1968.

Flashlamp Excited Organic Dye Lasers by B. B. Snavely, Proc. I. E. E. B,Volume 57, page 1374, 1969.

CW Operation of an Organic Dye Solution Laser by O. G. Peterson, S. A.Tuccio, and B. B. Snavely, Applied Physics Letters, Volume 17, page 245,1970.

In the laser pumped configuration, a gas laser is typically arrangedwith its output aimed at the dye cell of the dye laser through the highreflectance mirror of the dye laser. For efficient transfer of energyinto the dye laser, the mirror must be highly transparent to the outputof the gas laser. At the same time, to enable resonance in the dyelaser, the mirror must be highly reflective to light produced in the dyelaser. These requirements are not readily compatible with each other,and present a difficult design problem.

Briefly, according to the invention, the problem is resolved by using asingle mirror as both the output mirror of the pumping gas laser and thehigh reflectance mirror of the pumped dye laser. The design requirementsof the single, dual purpose mirror are easier to meet than therequirements for the high reflectance mirror of the dye laser as used inthe previ ously suggested arrangement, and improved efficiency ofoperation is achieved, as well as economy of construction.

Another feature of the invention relates to a relatively simplearrangement for tuning the dye laser, that is, for adjusting its outputto any desired wave length within the capability of the particular dyeused. The arrangement includes a lens having relatively largelongitudinal chromatic aberrations (a high dispersion characteristic) atthe output end of the dye laser for focusing the internally resonatinglight from the output mirror back onto the dye cell. The output mirroris formed on the surface of the lens opposite from the dye cell. Thewavelength of the light reflected from the output mirror and focused bythe lens at the reaction zone of the dye cell depends, because of theaberration, on the spacing of the lens from the cell, and motion of thelens toward and away from the cell thus changes the wavelength of thelight emitted by the laser. If desired, tuning can also be effected bychanging the tilt of an etalon plate mounted between the dye cell andthe output lens.

DETAILED DESCRIPTION A presently preferred embodiment of the inventionwill now be described in connection with the accompanying drawing,wherein the single FIGURE is a schematic diagram of a dye laseraccording to the presently preferred embodiment of the invention.

As shown, the dye laser 10 is arranged to be pumped by a gas laser 12.The output mirror 14 of the gas laser serves also as the highreflectance mirror of the dye laser. It is formed on the input lens 16of the dye laser on the surface facing the gas laser. Typically, themirror 14 is designed to transmit somewhat less than five percent of thelight generated in the gas laser and impinging on it and to reflect therest. As the high reflectance mirror of the dye laser, the mirror 14must reflect more than 99 percent of the light generated in the dyelaser and impinging on it. The transmission and reflectance requirementsare relatively easy to satisfy, and the design of the mirror 14 is arelatively simple matter. It is designed for maximum reflectance at allwavelengths of interest for the dye laser 10, and with a specifiedreflectance at the wavelength of the light generated in the gas laser12, so as to maximize the output of the gas laser.

The input lens 16 is designed for small chromatic aberration (minimumdispersion) so that it maintains both the pumping light and theresonating light always at the reaction zone of the dye cell 18throughout the tuning range of the dye laser.

An output mirror 20 is formed on the outer surface 22 of an output lens24, which is mounted for limited reciprocation along the main axis ofthe laser 10. The output lens 24 according to the invention has a largelongitudinal chromatic aberration (a high dispersion characteristic) andthus has different focal lengths for light of different respectivecolors. A change in spacing between the lens 24 and the dye cell 18changes the color of the light reflected from the output mirror 20 thatis focused in the reaction zone of the dye cell 18 and thereby changesthe wavelength of the light resonating in the laser 10 and emitted byit.

Tuning of the dye laser 10 may be done simply by moving the output lens24 toward and away from the dye cell 18. A piezoelectric crystal 34 mayconveniently be used for moving the lens 24 under fine control. Asshown, the lens 24 is secured on a slidable carrier 32, which is fixedto one surface of a piezoelectric crystal 34, the opposite surface ofwhich is anchored to a rigid support. The crystal 34 is energized by adc. voltage, causing it controllably to change its length thereby tomove the carrier 32 with the lens 24 selectively back and forth.

Optionally, for fine adjustments in tuning, an etalon plate 36 may bemounted between the dye cell 18 and the output lens 24. Changes in theangle of the etalon plate relative to the main axis of the laser changethe length of the optical path between the dye cell 18 and the outputmirror 20, thus effecting a change in the wavelength of resonance.

The windows 26 of the dye cell are preferably of nonpolarizing sapphire.Sapphire is well suited to withstand high temperatures that may beproduced in the cell 18, and, more importantly, anti-reflection filmscan be readily applied to it that are very effective. In accordance withthe usual practice, all of the light transmitting surfaces, except themirrors 14 and 20, are treated to minimize reflection.

The dye is circulated through the dye cell 18 in the usual way to removeheat produced in the cell. Typical dyes that are known to be suitablefor use indye lasers for focusing a selected one of said several areRhodamine B, Rhodamine 6G, and fluoroscein. wavelengths in said dyecell, and

What is claimed is: means for controllably moving said movable lensin 1. A tunable dye laser comprising: the direction of said longitudinaldispersion, a transparent dye cell containing 'a fluid substance therebyselecting a wavelength from said several capable of lasing at severalwavelengths, wavelengths. a laser excitation source, 2. The apparatus ofclaim 1 wherein said means for a pair of mirrors for reflecting lightemanating f controllably moving said movable lens is a piezoelectricsaid dye cell in response to the excitation source, crystal with avariable voltage pp y connected said light having a focal point in saiddye cell, at 10 thereto wherein motion motion of said crystal in leastone of said mirrors comprising a coating on a response to said Voltagels coupled to Sald movable movable lens having a chromatic dispersionlenscharacteristic longitudinally toward said dye cell 7414 lO60l2 0368

2. The apparatus of claim 1 wherein said means for controllably movingsaid movable lens is a piezoelectric crystal with a variable d.c.voltage supply connected thereto wherein motion motion of said crystalin response to said voltage is coupled to said movable lens.